The present invention relates to fungal inocula and their use in degrading and bioremediating wood treated with chemical preservatives. More specifically, this invention discloses and claims a fungal inoculum, the method of its preparation, and its use in degrading and bioremediating wood treated with chromated copper arsenate.
Wood used in the construction of today""s decks, docks and buildings, or as utility poles and railroad ties, is typically treated with a chemical preservative to prevent its deterioration and extend its service life. The chemical preservative used will generally depend upon the intended use of the wood and often includes chemicals such as chromated copper arsenate (CCA), ammoniacal copper quat (ACQ), creosote and pentachlorophenol. Of these preservatives, CCA is one of the most prevalent due to its minimal cost, and because it provides a dry and paintable surface after its application and leaves the wood relatively leach-resistant.
Treated wood is typically collected and stored at landfills or other facilities once it reaches the end of its useful life. Presently, large quantities of this waste wood is accumulating in landfills at an alarming rate. The collection and storage of such large quantities of waste wood in a single location creates an environment where the contamination of the surrounding soil and groundwater by toxic, environmentally-persistent chemicals is a likely result.
Contamination of soils and groundwater with toxic, environmentally-persistent chemicals is a serious problem. Toxic, environmentally-persistent chemicals are those that are resistant to degradation in the natural environment. As such, these chemicals pose a multi-faceted problem in that as they persist and accumulate in the environment, their toxicity, including in many instances, proven carcinogenicity, presents substantial health risks to both animals and human beings.
Environmental contamination from CCA-treated wood is a specific concern in view of the large volume of CCA-treated waste wood expected to be removed from service and disposed of in the near future. Although CCA-treatment is considered to be highly leach resistant, small amounts of Cu, Cr and As contaminates are still measurable in leach water and soils.
The prior art is replete with methods for degrading hazardous chemicals. However, this prior art is generally, and specifically, directed towards halogenated aromatic compounds. Suggested treatment strategies include incineration of the waste, removal and isolation of the contaminated materials, and degradation of the pollutant by bacteria.
All of these strategies suffer from serious deficiencies. Incineration is extremely expensive due to the required energy expense and the necessity of moving the contaminated material to remote locations. Incineration is also impractical because of the large quantities of waste which needs processing. Removal and isolation of the contaminated material is also expensive and does nothing to effect a long-term solution. Degradation of the chemicals using bacteria has also proven ineffective due to the bacteria""s specificity for particular chemicals and its sensitivity to the toxic chemicals and environmental conditions.
U.S. Pat. No. 5,476,788 employs another strategy which utilizes an inoculum containing lignin-degrading fungal species Phanerochaete chrysosporium, Phanerochaete sordida, or Trametes hirsuta to remediate solid materials, such as soils, sludge, sediments, and debris (e.g., woods), contaminated with pentachlorophenol. The inoculum contains one or more of the fungal strains and a lignocellulosic substrate, i.e., sawdust. In its use, the inoculum is combined with the pentachlorophenol-contaminated material and the entire mixture is aerated and hydrated until the inoculum metabolizes the pentachlorophenol to a less toxic product. Typically, this less toxic product includes pentachloroanisole.
Although the above-identified bioremediation strategy provides a useful means of reducing the pentachlorophenol content in various solid materials, it does not address the concerns associated with other wood preservatives currently used in the world today. Moreover, it fails to provide a working strategy for other types of fungal strains which require a more specific and unique environment to effectively remediate chemical preservatives such as CCA, ACQ, creosote, or pentachlorophenol or degrade wood treated with these chemicals.
The present invention is summarized in that it discloses a fungal inoculum, the method of its preparation, and its use in degrading and/or bioremediating wood treated with the chemical preservative chromated copper arsenate (CCA).
The disclosed fungal inoculum generally comprises of at least one CCA-tolerant fungus, a lignocellulosic substrate, and a nutrient supplement. The CCA-tolerant fungal strains are preferably selected from the group consisting of Meruliporia incrassata (TFFH-294), Antrodia radiculosa (MJL-630), Meruliporia incrassata (Mad-563) and Antrodia radiculosa (FP-90848-T). The lignocellulosic substrate is preferably sawdust or wood chips. Other feasible substrates are rice straw, corn stalks, and wheat straw. The nutrient supplement is preferably selected from the group consisting of corn steep liquor, cornmeal and wheatbran.
In one preferred embodiment, the fungal inoculum is prepared by first growing the CCA-tolerant fungus in dark, aerobic conditions, having a relative humidity and a temperature sufficient to support fungal growth. The fungus is then combined with a homogenous matrix comprising sterile water, the nutrient supplement, and the sterilized lignocellulosic substrate, to form the fungal inoculum. The fungal inoculum is then allowed to mature by exposing the mixture to dark, aerobic conditions, at a relative humidity and in a temperature range sufficient to allow the fungus to reach a confluent growth.
Waste wood containing CCA is remediated or degraded by inoculating the waste wood in the fungal inoculum. To inoculate the waste wood, the fungal inoculum is first spread over the waste wood until all of the waste wood is covered. The waste wood and fungal inoculum mixture is then aerated and hydrated for a time and under conditions sufficient to allow the inoculum to at least partially remediate the CCA and/or degrade the waste wood to a desired degradation product. In some instances, the degradation product may be capable of reuse in paper or wood composites, or simply have a reduced volume.
It is an object of the present invention to provide a method for bioremediating and/or degrading chemically treated waste wood to achieve a product having a reduced volume and/or the capacity to be reused as a wood fiber resource.
It is another object of the present invention to provide a fungal inoculum, and a method for preparing said fungal inoculum, which is useful in bioremediating and/or degrading chemically treated waste wood.
It is another object of the present invention to provide a fungal inoculum, and a method for using the fungal inoculum, to degrade and at least partially remediate waste wood chemically treated with CCA.
One advantage of the present invention is that the CCA-tolerant fungi utilized do not require genetic alteration to specifically grow in the presence of CCA. Thus, the introduction of the fungi into the environment provides no new, non-naturally occurring organisms.
Another advantage is that the preparation and use of the fungal inoculum is fairly simple and utilizes agricultural waste products and waste products from saw mills and urban chipping. These products have the additional advantage of providing a quick and low cost food source for the fungus, while having the added effect of stimulating rapid and extensive fungal growth, as well as providing a readily storable and transportable solid matrix.
Another advantage is that the inoculum and its method of use are particularly well suited for waste woods such as pressure-treated lumber from buildings, decks, utility poles and railroad ties. Specifically, the solid matrix of the fungal inoculum provides a wood environment for fungal growth which is similar to that of the waste wood. The fungal strain is, therefore, readily adapted to the waste wood environment upon inoculation and does not require a period of adjustment before degradation and bioremediation begins.
These and other objects and advantages of the invention are readily understood in view of the following detail description and examples.
Waste wood containing chromated copper arsenate (CCA) is degraded and remediated in accordance with the present invention by inoculating the waste wood with a fungal inoculum comprising at least one CCA-tolerant fungus, a lignocellulosic substrate and a nutrient supplement. The fungal inoculum is applied to the waste wood and maintained in an aerated and hydrated environment having temperature conditions and a moisture content sufficient to allow the inoculum to grow and at least partially remediate the CCA or degrade the preservative treated wood. The inoculum and the waste wood are combined until a degradation product is achieved that is either of a volume consistent with the desires of the practitioner or capable of being recycled and used for paper or other composite woods.
CCA-tolerant fungi according to the present invention are generally defined as fungi capable of surviving and sustaining growth while being exposed to CCA. In the preferred embodiment, the CCA-tolerant fungi include, without limitation, Meruliporia incrassata (TFFH-294), Antrodia radiculosa (MJL-630), Meruliporia incrassata (Mad-563) and Antrodia radiculosa (FP-90848-T). Most preferably, the fungus utilized is Meruliporia incrassata (TFFH-294). The CCA-tolerant fungi, however, may also include any other CCA-tolerant fungus capable of degrading or bioremediating the treated waste wood. Preferably, the chosen fungus should provide a twenty percent (20%) or more dry weight loss in the waste wood after about ten weeks of reaction time.
In the preferred embodiment, the CCA-tolerant fungi are naturally existing fungi and not genetically altered or conditioned to grow under specific conditions or in the presence of a particular preservative. It is anticipated, however, that one skilled in the art may use a genetically altered or conditioned fungus in accordance with the present invention. Genetically altered or conditioned fungi may include, but are not limited to, any fungus modified to grow in the presence of a specific nutrient supplement or food source.
In accordance with the Budapest treaty, the strains Meruliporia incrassata (TFFH-294), Antrodia radiculosa (MJL-630), Meruliporia incrassata (Mad-563) and Antrodia radiculosa (FP-90848-T) were deposited with the Agricultural Research Culture Center (NRRL), an International Depositary Authority located at 1815 North University Street, Peoria, Ill. 610604 U.S.A., on Jul. 30, 1999, and given the accession numbers NRRL 30165, NRRL 30169, NRRL 30171, and NRRL 30166, respectively.
The lignocellulosic substrate serves as a long-term food source for the fungal. inoculum as well as a matrix for its storage and handling. Generally, xe2x80x9clignocellulosic substratexe2x80x9d refers to a substrate having lignin, cellulose, or a combination of both lignin and cellulose. In the preferred embodiment the lignocellulosic substrate includes sawdust or wood chips, either alone or in combination, but may also include any substrate that is capable of sustaining the growth of the fungi. Other lignocellulosic substrates may include, without limitation, agricultural residues such as rice straw, corn stalk, wheat straw, etc.
Sawdust or wood chips are preferred, however, for several reasons: (1) they provide a long-term food source for the fungus while providing fungal growth in a wood environment similar to the CCA-treated waste wood environment experienced during inoculation; (2) they permit the production of a large quantity of fungi in a single container; (3) they provide a substrate for easily storing and transporting the fungi; (4) they provide a matrix for convenient and even distribution of the fungus at the inoculation site; and (5) they provide a low cost use of a waste product from saw mills.
The nutrient supplement is defined as a supplement for the lignocellulosic substrate which provides a food source that stimulates rapid and extensive fungal growth beyond that obtained from the lignocellulosic substrate alone. The nutrient supplement may be of any food source which accomplishes the above stated goal and may differ depending upon the fungus selected. Preferably, however, the nutrient supplement used is either a corn steep liquor, cornmeal or wheatbran.
Preferably, the fungal inoculum is prepared by first growing the CCA-tolerant fungus, or fungi, in culture containing malt extract agar: The culture is then typically incubated for one to two weeks, or until a confluent fungal growth is achieved over the agar surface. The incubation is best performed in dark, aerobic conditions, at a relative humidity of about 70%, and at a temperature range from about 20xc2x0 C. to 35xc2x0 C., and more preferably at a temperature range from about 27xc2x0 C. to 32xc2x0 C. 
After achieving a confluent fungal growth, the fungus, lignocellulosic substrate and the nutrient supplement are combined to form the fungal inoculum, or xe2x80x9cseeding.xe2x80x9d The lignocellulosic substrate is first heat- sterilized and allowed to cool. The sterilized lignocellulosic substrate is then mixed with the nutrient supplement and sterile water until a homogenous matrix is formed. The lignocellulosic substrate is preferably combined with the sterile water at 2-3 volumes of water per volume of substrate, while the nutrient supplement is added in a range from about 1% to 5% per volume water. Liquid nutrient supplement should always be added to the sterile water first and solid nutrient supplement should always be mixed with the substrate before adding the sterile water. This will ensure a homogenous matrix.
The homogenous matrix is gently mixed with the fungal culture and allowed to grow to form the final fungal inoculum. The mixture is allowed to grow for a time and under conditions which allow the fungus to reach confluent growth. Preferably, the mixture is grown in dark aerobic conditions, at a relative humidity of about 70%, and in a temperature range from about 20xc2x0 C. to 35xc2x0 C., and more preferably at a temperature range from about 27xc2x0 C. to 32xc2x0 C. Typically, confluent growth should occur within 4-8 weeks, but depends specifically upon the fungal volume introduced into the matrix, the lignocellulosic substrate, and the nutrient supplement. For example, a heavy fungal inocula with sawdust will shorten the period of fungal growth.
The fungal inoculum is ready for use or storage as soon as it has reached confluent growth. If immediate use is desired, the inoculum can be readily transported to the bioremediation and/or degradation site where it is applied to completely cover the waste wood. In the alternative, if storage is desired, the fungal inoculum can be stored at 4xc2x0 C. The storage at 4xc2x0 C. slows the fungal development and prevents overgrowth.
In one preferred embodiment of the present invention, large quantities of industrial inoculum can be produced either with large numbers of tray inoculum, or in large durable plastic bags with aeration patches to allow the appropriate airflow. Trays and bags can be transported easily to the field sites and applied on the waste wood. Production of inoculum directly in the truck or truckload container is also a possibility.
In another embodiment, steam is an alternative source for sterilization. This is especially useful in pilot plants where steam is readily available. In accordance with this embodiment, the steam provides both sterility and moisture content for the lignocellulosic substrate. After being steamed, however, the substrate temperature must be cooled so as to avoid killing the fungi.
Once transported to the bioremediation/degradation site, the fungal inoculum is spread over the waste wood until all of the waste wood is covered. Preferably the waste wood is heat sterilized prior to application so as to minimize other environmental factors which may effect the ability of the fungi to properly degrade or bioremediate the waste wood. Such factors typically include highly competitive bacteria or other fungi.
The CCA-containing waste wood and fungal inoculum mixture is then aerated and hydrated for a time and under conditions sufficient to allow the inoculum to at least partially metabolize the CCA and/or degrade the waste wood to a desired degradation product. The inoculated waste wood is maintained in a dark, aerobic environment, at a relative humidity of about 70%, and in a temperature range from about 20xc2x0 C. to 35xc2x0 C., and more preferably in a temperature range from about 27xc2x0 C. to 32xc2x0 C. The inoculation environment must have ample air space to ensure proper growth and to allow proper oxygen flow. In the absence of proper oxygen flow fungal growth will be hampered.
The degradation of the wood by the fungal inoculum will generally result in a degradation product having either a reduced volume or a reduced concentration of CCA. Such a product will provide a resource capable of reuse in paper or wood composites, or simply have a reduced volume such that storage or further processing is minimized.
The present invention is further explained by the following examples which should not be construed by ways of limiting the scope or spirit of the present invention.